    string solve(string s, string t) {
        // write code here
        int i=s.size()-1;
        int j=t.size()-1;
        string ans;
        int curr=0;
        while(i>=0 || j>=0 || curr)
        {
            int a=i>=0?s[i]-'0':0;
            int b=j>=0?t[j]-'0':0;
            int res=a+b+curr;
            curr=res/10;
            ans=ans.insert(0,to_string(res%10));
            i--;
            j--;
        }
        return ans;
    }